Thin-film transistor (TFT) liquid crystal display (LCD) devices typically include a display panel 11, a gate line driver circuit 12 and a data line driver circuit 10, as illustrated by FIG. 1. The display panel 11 typically comprises a two-dimensional array of display cells having TFT access transistors T1 therein which can be turned on when display data is being loaded from a respective data line DL 16 to a liquid crystal capacitor C1 within a selected cell. As illustrated, each liquid crystal capacitor C1 may be electrically connected in series between a drain/pixel electrode of a respective access transistor T1 and a common potential Vc. As will be understood by those skilled in the art, a row of access transistors can be turned on simultaneously during a selection time interval by driving a respective gate line 14 to a logic 1 potential. These and other aspects of TFT-LCD devices are more fully described in U.S. application Ser. No. 08/786,474, now U.S. Pat. No. 5,923,310, entitled "Liquid Crystal Display Devices With Increased Viewing Angle Capability and Methods of Operating Same", assigned to the present assignee, the disclosure of which is hereby incorporated herein by reference. Additional aspects of TFT-LCD devices are also disclosed in U.S. Pat. Nos. 5,793,346 entitled "Liquid Crystal Display Devices Having Active Screen Clearing Circuits Therein, U.S. Pat. No. 5,808,706, entitled "Thin-Film Transistor Liquid Crystal Display Devices Having Cross-Coupled Storage Capacitors", and U.S. Pat. No. 5,815,129, entitled "Liquid Crystal Display Devices Having Redundant Gate Line Driver Circuits Therein Which Can be Selectively Disabled", assigned to the present assignee, the disclosure of which is hereby incorporated herein by reference.
As will be understood by those skilled in the art, AC driving methods are typically used in TFT-LCD devices to inhibit display panel deterioration. Such AC driving methods include line inversion and dot inversion methods. Both of these methods require the use of data line driver circuits 10 which are capable of generating positive and negative polarity gray level voltages. The use of data line driver circuits which can generate gray level voltages having relatively small offset margins is advantageous because there is an inverse relationship between the magnitude of the offset margins and the number of shades of gray or color a display can generate.
Referring now to FIG. 2, a conventional 6-bit data line driver circuit is illustrated. This driver circuit is responsive to a polarity selection signal (POL) (which enables the AC driving method) and includes a decoder 20 which can generate 2.sup.6 =64 gray level voltages as inputs to an follower amplifier circuit 24. These gray level voltages may be provided as positive or negative signals having respective magnitudes in a range from 1-5 volts (i.e., the 4 volt range is divided into 64 levels). Operation of this follower amplifier circuit 24, which is also typically referred to as a unity gain amplifier, is more fully described in section 3.5 of a textbook by A. Sedra and K. Smith entitled "Microelectronic Circuits", Holt, Rinehart & Winston (1982). A panel capacitor C26 is also illustrated. The panel capacitor is representative of the combined load capacitance associated with a respective data line which is electrically connected to the source electrodes of a column of TFT access transistors T1.
Unfortunately, although conventional follower amplifier circuits 24 may be capable of providing a significant amount of current to a data line (DL) to thereby provide "hard" pull-up or pull-down during a selection time interval when data is being loaded into a row of display cells, such circuits 24 may only be capable of reproducing a gray level input voltage Vin on the data line (DL) to within .+-.20 mV of its target level. Accordingly, it may be difficult to obtain higher display resolution fidelity using larger decoders 20 (e.g., 8 bit decoders) because a 4 volt range having 2.sup.8 =256 levels would require much smaller offset margins on the order of .+-.5 mV.
Thus, notwithstanding the above-described TFT-LCD devices having data line driver circuits therein which can handle 6-bit data, there continues to be a need for higher resolution display devices.